The process disclosed in JP-A-1-201253 is among known techniques pertinent to production of a heat generating molded article using oxidation reaction of oxidizable metal powder with oxygen in air. According to the process, a raw material slurry is prepared by suspending a fibrous substance in water and adding thereto an oxidizable metal, e.g., iron powder, activated carbon as a moisture retaining agent, an electrolyte as a reaction assistant, etc. A fiber layer prepared from the slurry by a papermaking process is dewatered by suction and pressed into a heat generating molded article of sheet form having a water content of 5 to 65 wt %.
Because the electrolyte has previously been added into the slurry before papermaking, it is difficult to control the electrolyte content in the molded article obtained by papermaking and dewatering. Presence of the electrolyte, which is a reaction assistant, in the slurry can induce oxidation of the oxidizable metal as suspended in the slurry. It is more likely that oxidation of the oxidizable metal has started abruptly by the time when the watery fiber layer is subjected to dewatering and shaping. In order to suppress such an oxidation reaction, it has been necessary to take some countermeasures such as carrying out the production in an inert gas atmosphere, which makes the production equipment complicated.
JP-A-3-152894 discloses a technique comprising the steps of scattering oxidizable metal powder on a sheet substrate made up of irregularly accumulated fibers and having a large number of voids, vibrating the substrate to prepare a sheet structure having the oxidizable metal powder held in the inside of the substrate, and impregnating the structure with an electrolyte solution having activated carbon suspended therein.
According to this technique, however, since the activated carbon is in a suspended state in the electrolyte solution to be infiltrated into the structure, it is not allowed to penetrate deep into the structure. The resulting heat generating article has the oxidizable metal powder, activated carbon, and fiber dispersed therein non-uniformly. As a result, the heat generating article fails to exhibit satisfactory heat generation characteristics.
Accordingly, an object of the present invention is to provide a process of producing a heat generating molded article, which process enables easy control of the electrolyte content in the final product, minimizes the oxidation of the oxidizable metal during the production, and provides a molded article with satisfactory heat generation characteristics.